Current vehicles are equipped with functionality to assist steering operations performed by a driver. Examples of such steering assistance functionality include Lane Keep Assist Systems (LKAS) that cause a vehicle to travel in the substantial center of a lane, Lane Departure Warning (LDW) and Road Departure Mitigation (RDM) that warn of and suppress vehicle lane departure, and the like. LKAS executes lane keep assist control and LDW and RDM execute steering suppression control. Additionally, in recent years, Automatic Lane Change (ALC) systems that execute automatic lane change control are also being developed as steering assistance functionality.
Japanese Unexamined Patent Application Publication No. 2013-212838 (paragraphs [0100] to [0104]; claims 5, 7, and 9; and FIG. 8) describes a steering assistance device that generates supplementary torque for executing lane keep control. When a driver performs steering operation while lane keep control is being executed, this steering assistance device suppresses the supplementary torque and cancels lane keep control.
Japanese Unexamined Patent Application Publication No. 2012-226392 (paragraphs [0016] and [0018]) describes a driving assistance system that executes automatic lane change control when operation of a direction indicating device is detected while lane keep control is being executed. This driving assistance system executes automatic lane change control by changing a lane to be kept to a lane in an operation direction of a direction indicating device switch.